Plastic Seas

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Last summer, when filming for a series to be broadcast next year, a team from the BBC’s Natural History Unit saw first-hand how discarded plastic can end up thousands of miles away from where people live when they visited French Frigate Shoals, an island north west of Hawaii.

There they found turtles nesting amongst plastic bottles, cigarette lighters and toys. And they discovered dead and dying albatross chicks, unwittingly killed when their parents fed them plastic carried in as they foraged for food in the sea.

Some of the chicks die when sharp edges puncture their bodies, others from starvation as their stomachs fill with plastic they cannot digest.

We have known for a while that plastic is a threat to the albatross, but how dangerous is discarded plastic for other wildlife and could it affect us?

Some of the plastic in our oceans has been illegally tipped at sea, or is litter from fishing, most comes from the land, from poorly run landfill sites and industrial waste.

Floating debris is carried to the Hawaiian archipelago by giant rotating ocean systems, or gyres, partly driven by air currents.

Hawaii sits in the midst of a gyre known as the North Pacific Sub-tropical High. The North Pacific gyre is one of five gigantic interconnected systems of ocean currents. Each spirals around a central point, drawing material inwards.

These spirals can also eject material, out towards the Arctic and Antarctic, spreading plastic across the globe over time.

Plastic is made to last, so it decays only very slowly in the oceans, breaking down into ever smaller fragments. These tiny fragments are known as micro-plastic.

Hormonal changes

Dr Simon Boxall is an expert in marine pollution based at the National Oceanography Centre in Southampton, on Britain’s south coast. We took a boat trip with him in the sea near his research centre.

Using a simple net and bottle system, the boat filtered roughly 400 tonnes of water in 10 minutes. With the naked eye we could see mud, twigs and a few feathers, but when we looked at the sample under the microscope in Dr Boxall’s laboratory tiny pieces of plastic became clear.

The sample included small pieces of plastic rope and plastic bag, some fragments were distinctly coloured and some had sharp edges. There were pieces less than a millimetre across, similar in size to the living things in our sample – the phytoplankton, or tiny plants, and zooplankton, or tiny animals.

“There’s been a lot of research in the United States looking at how the plastic gets into the food chain, and certainly it’s been shown that it gets into bi-valves, mussels and oysters on the seabed, and it does have an effect on them,” Dr Boxall said.

“They bio-accumulate the plastic as they filter the water. That concentrates the plastic and effectively turns some of those molluscs into hermaphrodites. Some years ago it was assumed that it was like roughage, and didn’t have a major impact, but we know now that those very small plastic particles can mimic certain things like oestrogen,” he added.

Chemical adsorption?

However, he said the true effects are not yet known:

“These plastic particles are like sponges, they’re a bit like magnets for other contaminants, things like Tributyltin, the anti-fouling material. The tiny plastic particles absorb these materials and effectively become quite toxic. We don’t know yet whether that then has an impact on the human food chain. It’s still very early days to find out how far up the food chains these plastic particles go.”